In practical applications, it is usually assumed that the wave spectrum is of a single mode form, and well modelled by a JONSWAP or Pierson-Moskowitz spectrum. This assumption is of a reasonable accuracy for severe sea states. However, moderated and low sea states are often of a combined nature, consisting of both wind-sea and swell and should be characterized by a double peak spectrum. Bimodal seas can have a significant impact on the design and operability of fixed and floating offshore structures as well as LNG terminals. Although several separation procedures for the wave components exist the bimodal Torsethaugen spectrum is probably the only one well established in design work. This spectrum was developed primarily for one location at the Norwegian Continental Shelf (Statfjord Field) but in qualitative terms is expected to be of much broader validity. The present study discusses applicability of the Torsethaugen spectrum for locations outside the Norwegian Continental Shelf and uncertainties related to use of the spectrum.

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